Removed inaccuracte information on message type content

[jamestynan-content]

Description

Update content across the following pages to correct inaccurate guidance on fallback behavior and fallback timeframes:

/about/campaigns
/about/event-based-messaging
/about/direct-messaging

The changes are:

• All pages: Removed references stating that fallbacks occur when a 'notified' status is not received. Notify does not support this.
• Direct messaging page: Removed the 12-hour option for acute secondary care appointment messages as this is no longer accurate. Integrators can only select 4 hours or 24 hours.

Type of changes

• [x ] Refactoring (non-breaking change)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would change existing functionality)
• Bug fix (non-breaking change which fixes an issue)

Checklist

• [x ] I am familiar with the contributing guidelines
• [x ] I have followed the code style of the project
• I have added tests to cover my changes
• I have updated the documentation accordingly
• This PR is a result of pair or mob programming

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Sensitive Information Declaration

To ensure the utmost confidentiality and protect your and others privacy, we kindly ask you to NOT including PII (Personal Identifiable Information) / PID (Personal Identifiable Data) or any other sensitive data in this PR (Pull Request) and the codebase changes. We will remove any PR that do contain any sensitive information. We really appreciate your cooperation in this matter.

• [x ] I confirm that neither PII/PID nor sensitive data are included in this PR and the codebase changes.